Carbon Found To Leak From Land To Water
June 11, 2013

Land-Ocean Aquatic Continuum Must Also Be Considered For Future Carbon Storage Estimates

April Flowers for - Your Universe Online

In general, scientists have thought that about half of the carbon emitted by human activities remains in the atmosphere, with the other half being stored in the oceans and on land. A new study, published in Nature Geoscience, suggests that human activity might be increasing the transition of carbon from land to rivers, estuaries and the coastal zones. This indicates that large quantities of anthropogenic carbon might be hidden in previously unconsidered regions.

The study, led by the Université Libre de Bruxelles, the University of Exeter, Laboratoire des Sciences du Climat et l'Environnement, the University of Hawai'i and ETH Zürich, has revealed that increased leaching of carbon from soil — in large part due to deforestation, sewage inputs and increased weathering — has resulted in less carbon being stored on land. Instead, more is being stored in rivers, streams, lakes, reservoirs, estuaries and coastal zones. These environments are collectively known as the “land-ocean aquatic continuum.”

The research team reviewed prior data to show that a significant fraction of the carbon emitted through human activity that is taken up by the land is not actually stored there. Rather, it is stored in the aquatic continuum.

Pierre Regnier from Université Libre de Bruxelles said, "The budget of anthropogenic CO2 reported by the Intergovernmental Panel on Climate Change (IPCC) currently does not take into account the carbon leaking from terrestrial ecosystems to rivers, estuaries and coastal regions. As a result of this leakage, the actual storage by terrestrial ecosystems is about 40% lower than the current estimates by the IPCC."

Before this study, the land-ocean aquatic continuum wasn´t considered an important carbon sink. With this new data, however, future assessments of carbon storage must take the surface areas of the land-ocean aquatic continuum into account, in order to ensure accurate estimation of carbon storage. Future estimates will also require an improved knowledge of the mechanisms controlling the degradation, preservation, and emissions of carbon along the aquatic continuum to completely understand the impact of human activity on carbon transfer.

"Carbon storage in sediments in these rivers and coastal regions could present a more secure environment than carbon stored in soil on land. As soil warms up stored carbon can be lost to the atmosphere. The chances of this occurring in wet sediments are reduced,” said Professor Pierre Friedlingstein from the University of Exeter.

Of all the carbon that leaches from land to the land-ocean aquatic continuum, only a fraction is emitted back into the atmosphere. Another fraction is sequestered in sediments along the continuum. According to the study, only about 10 percent eventually reaches the open ocean.

Philippe Ciais from the Laboratoire des Sciences du Climat et l'Environnement said, "Our revisited global carbon budget which includes the land-ocean aquatic continuum is still entailed with significant uncertainties. It is however fully consistent with the observed growth rate of atmospheric CO2. Our downward revision of the land carbon storage is also in agreement with very recent results from forest inventories."

The team reports that a significant part of the carbon storage thought to be offered by ecosystems on land — mainly in forests — is negated by this leakage of carbon from soils to aquatic systems, and the atmosphere.